Don't write off VXI

Earlier this year, I attended a presentation on PXI instrumentation. Before the session, the presenter told me "VXI is dead, and PXI will replace it." Sorry, sir, but VXI isn't dead; it's just out of sight.

These days, I see few new VXI product introductions. Wondering about that, I asked several VXI instrument makers if they still produce new instrument modules and chassis. They do, but the people I talked to admit they haven't done a good job at announcing new products. The VXIbus Consortium (www.vxibus.org) and its member companies have started to come out from hiding. Still, they must do a better job informing customers and the press about new products. That should help quell the misconception that VXI is dead.

VXI holds an important place in test-and-measurement applications. Test engineers, particularly those who test military and aerospace equipment, have settled on VXI because of its performance-to-size ratio. VXI-based systems also perform functional tests on a range of commercial products. Recently, demand for VXI-based test equipment has increased, mostly because of increased defense spending. People at VXI equipment manufacturers say that two years ago, about 70% of their products went into testers for commercial products (mostly telecom), with about 30% going to military and aerospace companies. Today, those numbers are reversed.

VXI test-equipment makers also report a recent surge in orders to replace instrument modules in early VXI-based testers. Some test systems are more than 10 years old. Engineers want the better measurement performance that new VXI modules can deliver without losing software compatibility with existing systems.

Will PXI replace VXI? No, because instrument designers just can't fit the same functions on a 3U-size PXI card that they can put on a C-size VXI card. That's especially true for switching cards, because test engineers need the maximum number of switches per available space.

PXI enthusiasts argue that the bus moves more bytes per second than the VXI bus does. That's true, but in most functional-test applications, VXI's 40 Mbytes/s is more than fast enough. If bus speed were a great issue in test systems, then IEEE 488, with its top speed of 1 Mbyte/s, wouldn't remain popular.

PXI has established a place in the test equipment market. It works well in small test-and-measurement applications, but it won't replace VXI in large test applications. The two instrumentation buses will coexist for a long time. VXI equipment manufacturers just need to keep reminding us about new products and developments in VXI software or bus standards.

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